Hi,
I have come across a couple of interesting @longdesc use cases. The
first is by Laura Carslon which used "A11y Resolved Bug Comparisons"
graphs and pie charts. Describing a pie chart and graph like the
examples Laura provide would be extremely difficult without an attribute
like @longdesc, if you don't want the descriptions to appear inline. [1]
To expand on this problem, the need for an off page long descriptor is
made even clearer in the following example from 2006 (courtesy of Prof.
Barry McMullin of DCU) which he describes as a "Double-negative use
case". [2]
To explain - I will quote Barry directly from the CFIT website.
"Double-negative" because longdesc is not being used here â€” but I would
have liked to use it, and its use would have been absolutely
appropriate! It's just that weak user-agent support meant that using it
would potentially have left the long description actually unavailable to
people who might benefit from it. So instead, I decided to compromise
(somewhat) the experience of people who already could perceive the
graphical image perfectly well, and exposed the long description for all
users (even though it is redundant for the majority). This decision
then, logically, had the further effect of requiring an explanation â€”
for those majority users â€” of what a long description is and why â€” which
explanation, in turn, is redundant for those users who would normally
actually benefit from a long description!
I humbly suggest that such a convoluted (nay, "traumatic"!) design
decision â€” genuinely existing "in the wild" â€” should count as legitimate
evidence of the use-case-need for longdesc!?" [3]
To me the above example, compounds the first and illustrates that an off
page long descriptor is very much needed but due to the authors concerns
about UA support etc he decided /not/ to use it. This implies that:
1) A long descriptor, that can potentially reference a URI and can be
recognised and handled in a way that is conducive to a positive user
experience for an AT user is actually needed.
1) The consequences of having to include a very verbose description
inline can be problematic in terms of page bloat, potential perceived
complexity for users with cognitive disabilities and possibly other
usability issues, such as general confusion as to the descriptions
purpose for non-users of AT.
Josh
[1] http://www.d.umn.edu/~lcarlson/html5bugchart/20100821/
[2] http://www.aishe.org/readings/2007-1/No-14.html#x20-19300014.6
[3] http://www.cfit.ie/news-and-commentary-archive/525-longdesc-rip